ABSTRACT
All organelles are structurally well-characterized in the fixed and dehydrated state by electron microscopy. The study of most of their details in the living cell was, however, impossible for almost all but the largest organelles due to the limited resolution of light microscopy. When using visible light, this limit is around 200 nm, thus making the observation of most organelles such as secretory vesicles, synaptic vesicles, peroxisomes, smalllysosomes, and essentially all cytoskeletal filaments, such as actin filaments (6 nm diameter), intermediate filaments (10 nm), and microtubules (25 nm), impossible. Considerable progress in the study of cytoplasmic structures and their dynamics had, therefore, to await new techniques capable of visualizing these structures, identifying their chemical nature, and quantitatively analyzing their dynamic behavior.
